Atherosclerosis is a major cause of morbidity and mortality among both men and women. Multiple systemic risk factors, including hypertension, diabetes mellitus, smoking, and 1ipoprotein disorders are involved in the pathogenesis of this chronic inflammatory disease of arteries, but to date, it has not been possible to associate the risk factors with common pathogenic mechanism. Recent evidence suggests that a small group of transcription factors may be critical in linking the diverse risk factors to the initiation of the atherosclerotic lesion. This project emphasizes one of these transcription factors, nuclear factor-kappaB (NF-kappaB), whose activation has been linked to the onset of atherosclerosis through a remarkable series of correlations. These include observations that activated endothelial NF-kappaB is found predominately in atherosclerotic lesions where NF-kappaB-dependent endothelial genes are also selectively expressed; atherosclerosis develops in response to diverse stimuli that share the ability to create oxidant stress and activate the NF-kappaB system; several agents inhibiting lesion formation also act as antioxidants and stabilize NF-kappaB and; atherosclerotic lesions form at distinct regions of the arterial tree, especially at or near branch points or major curvatures where the endothelial NF-kappaB system is selectively activated. Although these correlations are provocative, there is no direct evidence demonstrating that NF-kappaB activation is necessary or sufficient for atherosclerosis or for defining lesion-prone regions. The goal of this proposal, therefore, is to determine the role of endothelial NF-kappaB in initiation of the atherosclerotic lesion. Unfortunately, loss of function mutants of several NF-kappaB system components in mice present significant developmental abnormalities precluding their use for studies of atherosclerosis. In this application, strategies using conditional mouse genetics are proposed to avoid this complication and test the hypothesis that the NF-kappaB system plays a key role in the formation of the early atherosclerotic lesion. In the First Specific Aim, the LDLR-/- mouse model of atherosclerosis will be used to determine if NF-kappaB expression is required for early lesion formation in vivo. These studies utilize the Cre-loxP system to achieve endothelial -restricted conditional mutation of NF-kappaB system components. In the Second Specific Aim, we will determine if dysregulated expression in endothelium of a gene that normally inhibits NF-kappaB activation alters early lesion formation in LDLR-/- mice. These studies will use tetracycline-regulated transgene expression to generate mice with inducible and endothelial-restricted expression of an inhibitor of NF-kappaB activation. In the Third Specific Aim, we will determine if NF-kappaB signaling plays a role in specifying lesion prone and lesion resistant regions of aorta in LDLR-/- mice. Taken together these studies should determine if the NF-kappaB system is necessary and/or sufficient for the initiation of the atherosclerotic lesion.